Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the engine, the heated coolant then circulated through a radiator to dissipate the heat. The cooling system may include various components such as a coolant reservoir coupled to the system for degassing and storing coolant. A pressurized reservoir that also serves to separate entrained air from the coolant is typically called a degas bottle. When the temperature of coolant anywhere in the system rises, thermal expansion of the coolant causes pressure to rise in the degas bottle as the trapped air volume reduces. Pressure relief can be achieved by releasing air from the degas bottle through a valve that is typically mounted in the fill cap. Then, when the temperature and pressure of coolant drops below atmospheric pressure in the degas bottle, air may be drawn back into the bottle through another valve that is often mounted in the fill cap.
If the coolant level in bottle is too low, the air volume will be too large to build sufficient pressure to prevent boiling and cavitation at the water pump inlet. At low fluid levels, the degas bottle will also no longer be able to separate air from the coolant and air can be drawn into the cooling system, again leading to poor cooling performance. If an overflow system is employed instead of an active degas system, a similar loss in cooling system performance can be realized when fluid levels are low.
Various approaches may be used to estimate fluid level in a reservoir. One example approach described by Murphy in U.S. Pat. No. 8,583,387 uses an ultrasonic fluid level sensor installed at the bottom of a reservoir to estimate a fluid level of the reservoir. However, the inventors herein have recognized that in such a cooling system, the dimensions of the coolant reservoir may vary based on the temperature of coolant contained in the reservoir. As a result, there may be inconsistencies in the estimated coolant level. Additionally, due to the location of the sensor at the bottom of the container, at low coolant levels, it may be unclear whether the fluid level in the reservoir is low or empty. Further still, it may be difficult to differentiate actual low coolant levels from incorrect coolant level estimation due to sensor degradation. In another example approach, described by Gordon et al in US 20130103284, the sensor is coupled to a coolant reservoir hose. One issue with such an approach is that the sensor can only detect the presence of coolant at that location in the circuit. Critical components of the power train may not be receiving coolant despite the presence of coolant in one of the coolant reservoir hoses, particularly if that hose is isolated from the cooling system by a valve (e.g., the engine thermostat hose). Further, while an indication of low coolant fluid level is received, engine temperature control may already be degraded due to substantial emptying of the coolant reservoir.
In one approach, the above issue may be at least partly addressed by a method for a coolant system, comprising: periodically transmitting a sensor signal from a bottom to a top of a vertical, hollow tube fluidically coupled to the reservoir at each of the bottom and the top; receiving an echo of the transmitted signal; and adjusting a power of the periodically transmitted signals based on an average duration elapsed between the transmitting and the receiving. In this way, the amount of power supplied to the piezoelectric transducer may be selectively increased to maintain the number of first-order echo returns above a first threshold, or selectively decreased to maintain the number of higher-order echo returns below a second threshold and maintain energy efficiency.
As one example, an engine coolant system may include a vertical tube aligned with a coolant overflow reservoir, the tube housing an ultrasonic sensor. The vertical tube may be coupled to the coolant reservoir at each of a top and bottom location via hoses, coolant flowing between the tube and the reservoir via the hoses. The hoses may be connected such that a headspace is generated between the top of the fluid level in the vertical tube and the top of the tube. In addition, the hoses may be connected such that the top of the vertical tube is arranged at a lower height than the top of the coolant reservoir, thereby allowing the sensor to more reliably estimate the fluid level in the reservoir and distinguish between low and empty coolant level states. The sensor, positioned inside a recess at the bottom of the vertical tube, may transmit a signal to the top of the vertical tube, an echo of the signal being received at the sensor after being reflected off the top of the tube. The signal may be transmitted periodically and based on an average echo time (which is the time elapsed between the signal being transmitted and an echo of the signal being received), the coolant level in the vertical tube may be estimated. This estimate may then be used to infer the coolant level in the reservoir. As one example, the sensor may receive first-order echo returns for each emitted pulse, but receive a number of second and third-order echo returns above a threshold number. In response to the detection of higher order echoes, the power supplied to the piezoelectric element may be decreased at a slower rate. At a later time, if the number of first-order echo returns falls below a threshold number, the power supplied to the piezoelectric element may be increased at a faster rate. In another example, the sensor may receive no first-order echo returns in a measurement period, in which case the power may be increased to the physical maximum until a threshold number of first-order echo returns are received in a measurement period.
In this way, an accuracy and reliability of determining a coolant level of a coolant overflow reservoir can be increased. By inferring the coolant level of the reservoir based on an estimated coolant level of a standpipe coupled to the reservoir, wherein the coolant level of the stand pipe is based on an echo time of an ultrasonic signal transmitted by a sensor of the stand pipe, inaccuracies in coolant level estimation due to distortion of an in-tank sensor output during thermal fluctuations, or vehicle motion, is reduced. By adjusting the energy output of the ultrasonic sensor based on the detection of first-order and second order echo times, sensor output optimization is achieved. Specifically, first order echo values can be improved while reducing the power requirement of the sensor. Overall, power reduction benefits are achieved without degrading the accuracy and reliability of coolant level estimation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.